The invention relates to a releasable and stress-free securing assembly for an optical element positioned in a centered manner in a mount. The optical element is provided, in the border region which is to be retained, with a beveled surface inclined in the direction of the mount. The mount has a groove which is open axially in front of the optical element, and a ring element which is elastically deformable in the axial direction is pressed in between the beveled surface and groove.
A securing assembly of this type is known from German Publication DE 29 22 287 A1. A lens positioned in a centered manner in a mount body is retained by an elastic ring, running in the vicinity of the circumference, under elastic prestressing against an axial abutment of the mount body. The ring consists of a rubber-like elastic material and is pressed into a ring groove of the mount body. The ring groove is partially overlapped in the axial direction by the circumferential surface of the lens. The cross section of the ring groove is intended to be at least of the same size as that of the ring, and it is to be possible for the lens to be inserted even if the ring has been placed in position beforehand. Possible shapes specified for the ring groove are rectangular, semicircular and trapezoidal cross sections, that is to say, shapes which enclose the ring in an essentially convex manner.
German Publication DE 1 113 101 PS also discloses such a securing assembly in which the ring groove corresponds precisely to the cross section of the pressed-in ring. On the mount body, it is intended to arrange, above the ring groove, an inwardly oriented, obliquely positioned peripheral surface which may be interrupted in the form of bayonet-like lugs.
Although these securing assemblies have already been known for decades, they have not gained widespread acceptance in practice.
A securing assembly which is comparable as far as outlay for, and processing of, parts are concerned involves the optical element being secured by a snap ring engaging in a groove in the mount. The snap ring usually consists of metal and may be of a circular or rectangular cross section. The depth of the groove and the snap-in depth of the snap ring in the radial direction are coordinated with one another. The height of the lens border and the position of the adjacent groove likewise have to be adapted to one another with great precision in order that the lens fit is neither too loose nor too tight. It is only possible to compensate for tolerances by way of costly follow-up work. It is not possible to compensate for dimensional tolerances produced by temperature fluctuations. Removal of the snap ring without scratching the lens surface is only possible if extreme care is taken. However, in particular in the case of optical systems made up of a number of elements, subsequent removal is necessary if particles of dirt are found in the system following assembly.
It is known, from German Utility Model 1 966 392, to provide above the lens, positioned in a centered manner, in the mount body a conically shaped groove into which there is inserted a plastic snap ring which has a correspondingly shaped conical facet. The conical abutment surface produces a contact-pressure force which acts in the axial direction, counteracts loosening of the snap ring and compensates for production tolerances in the groove. Since the snap ring consists of plastic, the risk of the lens surface being scratched is avoided.
It is also the case that this type of securing assembly has not been able to gain widespread acceptance.